1. Technical Field
The present invention relates to a paper conveyance device for continuous paper, and to a printer having the paper conveyance device.
2. Related Art
Folded continuous paper with sprocket holes, commonly known as fanfold paper, is used as a recording medium in business printers, a type of printing device. Fanfold paper is perforated between each page so that it can be severed, and is stored in a stack in the paper supply unit of the printer with the pages alternately folded in opposite directions at the perforations. Fanfold paper is conveyed by a paper conveyance mechanism with a tractor.
The tractor has tractor pins (engaging units) that can be inserted in the sprocket holes (engagement holes) formed in the paper feed direction of the continuous paper; a tractor belt having the tractor pins formed with a specific interval there between on the outside surface; and a drive sprocket and follower sprocket on which the tractor belt is mounted. The continuous paper is set so that the tractor pins are inserted in the sprocket holes. When the continuous paper is set, the tractor causes the tractor belt to turn by driving the drive sprocket rotationally by means of drive power from a drive source, and conveys the continuous paper while causing the tractor pins to sequentially engage the sprocket holes of the continuous paper. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2006-232470.
The paper conveyance device of a business printer that records information on continuous paper has a feed roller near the print head in addition to the tractor described above, and feeds the continuous paper in increments of a specific feed distance by synchronously driving the feed roller and the tractor. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2009-119574.
Fanfold paper used as continuous paper includes multipart forms made with carbonless paper using a leuco dye and developer reaction, for example, or carbon paper having a carbon ink coating on the back of the paper. When pressure is applied to carbonless paper or carbon paper by the metal pins of the dot impact head of an impact printer, for example, color is produced where pressure is applied, and information is printed in duplicate.
Applications for business printers have expanded in recent years, including, for example, the desire to print a wider variety of information and image information. As a result, printing with greater precision and higher density is desired. Many different kinds of recording media are also used, and it is desirable to, for example, use fanfold paper having sheets of different materials for prescription bags so that information can be printed on the envelope while feeding the paper through a business printer. High precision paper conveyance is therefore desirable.
The paper conveyance mechanism described above is also subject to variation in the paper feed distance of the tractor and the paper feed distance of the feed roller due to deviation in parts precision, for example. In addition, when the fanfold paper consists of two combined sheets of different kinds of materials, the paper feed distance of the portion to be printed can also vary due to differences in the friction coefficients of the sheets or differences in the coefficient of expansion caused by humidity. A problem is that variation in the paper feed distance leads to a drop in print quality.